Four persons died of asphyxiation after inhaling methane gas during "maintenance work" at a sewage tank in the Hyundai car factory at Irrungatukottai near Kancheepuram, fire service officials said.

Another person, who also took ill, has been admitted to a private hospital in Chennai and his condition was stated to beout of danger, they said.

The incident occurred at the second stage plant on Friday night when the five contract employees were attempting to clean up the sewage tank, which was used to store wastes of paints and other chemical materials, the officials said.

Initial reports this morning said there was a fire accident in the plant, but later the fire service clarified that it was an incident of asphyxiation.

Fire service officials attributed the mishap to "neglect" in undertaking maintenance work.